Rheumatoid arthritis (RA) is a chronic inflammatory disease of uncertain etiology. Since the cause is unknown, treatment has been directed at suppressing the signs and symptoms of chronic inflammation. Although many agents have been documented to decrease pain and swelling temporarily, none has been shown to have a major impact on the course of the disease. While therapeutic modalities have been developed for treatment of this disease.sup.1-4, uniform and persistent suppression of this condition has not been reported. Although current approaches remain promising, alternative means of drug development seem warranted and could yield not only new and effective treatment modalities, but also provide new insights into disease pathogenesis that could serve as the basis of future therapeutic innovations.
An area to search for new therapeutic interventions for different forms of arthritis, and particularly RA and other autoimmune diseases, is that of traditional Chinese medicines. One of these traditional medicines is from Tripterygium wilfordii Hook F, a shrub-like vine from the Celastraceae family .sup.5. Tripterygium wilfordii Hook F is known to contain a number of constituents, some of which appear to be toxic .sup.6. It is known that the leaves, stem, flowers, and the skin of the roots are poisonous and that ingestion can cause death .sup.7-9. In contrast, the woody portion of the roots of the plant is much less toxic. An extract of Tripterygium wilfordii Hook F prepared from the root of the plant, designated T.sub.2, has been described in the Chinese literature for the treatment of autoimmune diseases.sup.10-26. The preparation appeared to contain therapeutic components, and to have a reduced toxicity compared to other available preparations of the plant.
The T.sub.2 extract has been evaluated in a double-blind placebo controlled cross-over study involving 70 RA patients, these patients having had a mean duration of RA of 6 years .sup.10-11. Significant improvement in a variety of clinical parameters, particularly ESR, CRP, and Rheumatoid factor titers, was noted after 12 weeks of therapy in the experimental group compared with either baseline measurements or the placebo treated group. Of the patients treated, 82-93% noted improvement in different clinical criteria or laboratory correlates of inflammation. An immunosuppressive activity of T.sub.2 may be inferred from the finding that treatment induced inhibition of the production of IgM and IgM rheumatoid factor by the patients' peripheral blood mononuclear cells in vitro.sup.7. Toxicity, which consisted primarily of skin rash, gastrointestinal complaints and amenorrhea, was reportedly of a generally mild nature, and reversible with cessation of therapy.
The Chinese experience suggested that a daily dosage of 0.8-1.5 mg/kg of T.sub.2 was relatively safe and effective. Acute and chronic toxicity studies have been carried out with T.sub.2 in China using a variety of animal models. The LD.sub.50 of T.sub.2 in mice was found to be 159.7.+-.14.3 mg/kg.sup.27. The major chronic toxicity noted in rats administered 30 mg/kg for 90 days was azoospermia and decrease in testicular weight.sup.27. Lower dosages of T.sub.2 did not cause decreases in testicular weight. The toxicity studies, therefore, suggested that T.sub.2 exhibited a reasonable safety index and should be able to be administered to patients safely.
Research has begun in China to determine the spectrum of activity of various preparations of T. wilfordii. According to the reported results of these studies, extracts of TwHF were able to inhibit E-rosette formation by guinea pig T cells, mitogen induced IL-2 production by mouse T cells and antigen stimulated migration of rat lymphocytes.sup.28, 29. Components of T. wilfordii hook F known as triptonide and triptolide have been reported to inhibit the proliferation of lymph cells induced by concanavalin A.sup.30. Chloroform/ethanol extracts of the plant, referred to as T.sub.2 in the literature, have been described as having significant activity in vivo against certain mouse leukemias and in vitro against cells derived from human carcinomas.sup.31. The capacity of T.sub.2 to suppress a number of animal models of autoimmune disease, including adjuvant arthritis and experimental allergic encephalomyelitis, has been reported.sup.28-29, 32-36. Large concentrations of T.sub.2 preparations (30 mg/kg) have been reported to suppress delayed-type hypersensitivity reactivity in mice and may also suppress graft-versus-host disease, as well as skin and heart allograft rejection.sup.6,32. It remains unclear whether lower, more pharmacologically appropriate concentrations would also exert therapeutic effects in these animals, however.
The T.sub.2 examined in the Chinese literature is a crude extract containing a mixture of materials, including various glycosides, alkaloids, and diterpenoids. The active principle, however, has not yet been identified. A few components have been purified, including triptolide, wilfordine, and related compounds, but no particular purified component which accounts for the therapeutic or immunosuppressive activity of T.sub.2 exists.sup.40. High concentrations of triptolide were reported to suppress B and T lymphocyte proliferation and interleukin-2 production by mouse spleen cells.sup.41. However, the concentrations of the T.sub.2 used were sufficiently high that significant nonspecific toxicity undoubtedly occurred.
A number of pharmacologic agents have been used to treat rheumatoid arthritis and other inflammatory conditions. Among these are non-steroidal anti-inflammatory drugs (NSAIDS) and glucocorticoids. A major aspect of the mechanism of action of nonsteroidal anti-inflammatory drugs is generally thought to be the inhibition of cyclooxygenase, the enzyme responsible for the biosynthesis of some prostaglandins and certain related autacoids. This inhibition is dependent upon the drug reaching the cyclooxygenase enzyme, indicating that the mode of action is at the level of interaction with the enzyme protein itself. For example, acetaminophen can block the enzyme only in an environment that is low in peroxides which may explain its poor anti-inflammatory activity since sites of inflammation usually contain high concentrations of peroxides generated by leukocytes. Aspirin acetylates a serine at or near the active site of cyclooxygenase, inhibiting the enzymatic activity. The most common unwanted side-effect of NSAIDS and other aspirin-like drugs is a propensity to induce gastric or intestinal ulceration. More serious side-effects, such as anemia from resultant blood loss, may also sometimes occur.
Glucocorticoids have the capacity to prevent or suppress the development of the manifestations of inflammation. They are also of immense value in treating diseases that result from undesirable immune reactions. The immunosuppressive and anti-inflammatory actions of the glucocorticoids are inextricably linked because they both result in large part from inhibition of specific functions of leukocytes, in particular, inhibition of lymphokines.
Two categories of toxic effects are observed in the therapeutic use of adrenocorticosteroids.sup.76 : those resulting from withdrawal and those resulting from continued use of large doses. Acute adrenal insufficiency results from too-rapid withdrawal of these drugs. Prolonged therapy with corticosteroids may result in suppression of pituitary-adrenal function that can be slow in returning to normal. Further complications resulting from prolonged therapy with corticosteroids are: fluid and electrolyte disturbances; hypertension; hyperglycemia and glycosuria; increased susceptibility to infections; including tuberculosis; peptic ulcers, which may bleed or perforate; osteoporosis; a characteristic myopathy; behavioral disturbances; posterior subcapsular cataracts; arrest of growth; and Cushing's habitus, consisting of "moon face", "buffalo hump," enlargement of supraclavicular fat pads, "central obesity," striae, ecchymoses, acne, and hirsutism.
An object of the present invention is to provide preparations of T. wilfordii Hook F, and isolated components thereof, for the treatment of inflammation and for immunosuppression without steroidal agonist effect. Current NSAID treatment modalities are accompanied by significantly undesirable side-effects. Therefore, agents that have the anti-inflammatory effects of NSAIDS without the side effects would be of great benefit. A second object of the present invention is to suppress the production of prostaglandins and other related autocoids without encountering the side effects of common NSAIDS. Accomplishment of these objectives will provide improved methods for treating inflammation, and immunosuppression, such as in the treatment of autoimmune disease, and particularly rheumatoid arthritis.